Two types of elements have previously been known that make use of the deflection properties of piezoelectric ceramics; one is of the unimorph type in which a single thin layer of a poled piezoelectric ceramic material is adhered to a fixed electrode plate (shim); the other is of the bimorph type in which a thin layer of a poled ceramic is adhered to both sides of the shim.
These devices suffer from two major problems: if a high instantaneous negative voltage is applied or if negative voltages are applied for a prolonged period, either the piezoelectric ceramic material is depolarized or the adhesive between the ceramic material and the electrode material deteriorates such as to cause them to separate from each other. As a result, the life of these elements that are used as actuators is inevitably short.
The present inventors have discovered a piezoelectric ceramic material that can be described as a monomorph-type ceramic in that a single layer of this material is capable of deflecting without preliminary poling. The problems associated with the prior art can be effectively solved to a significant extent by using such monomorph-type piezoelectric ceramics as actuators.